Many companies and other organizations operate computer networks that interconnect numerous computing systems to support their operations, such as with the computing systems being co-located (e.g., as part of a local network) or instead located in multiple distinct geographical locations (e.g., connected via one or more private or public intermediate networks). For example, data centers housing significant numbers of interconnected computing systems have become commonplace, such as private data centers that are operated by and on behalf of a single organization, and public data centers that are operated by entities as businesses to provide computing resources to customers. Some public data center operators provide network access, power, and secure installation facilities for hardware owned by various customers, while other public data center operators provide “full service” facilities that also include hardware resources made available for use by their customers. As the scale and scope of typical data centers has increased, the tasks of provisioning, administering, and managing the physical computing resources have become increasingly complicated.
The advent of virtualization technologies for commodity hardware has provided benefits with respect to managing large-scale computing resources for many customers with diverse needs, allowing various computing resources to be efficiently and securely shared by multiple customers. For example, virtualization technologies may allow a single physical computing machine to be shared among multiple users by providing each user with one or more virtual machines hosted by the single physical computing machine, with each such virtual machine being a software simulation acting as a distinct logical computing system that provides users with the illusion that they are the sole operators and administrators of a given hardware computing resource, while also providing application isolation and security among the various virtual machines. Furthermore, some virtualization technologies are capable of providing virtual resources that span two or more physical resources, such as a single virtual machine with multiple virtual processors that spans multiple distinct physical computing systems.
Although the use of virtualization technologies has resulted in many advantages, the facts that many different virtual machines or compute instances are often implemented using the same physical resources, and that hundreds or thousands of such instances may be co-located within a single data center, may also have some potential negative side effects. One such problem may result from inadvertent timing coincidences associated with batch jobs (e.g., administrative scripts typically run without user interaction) scheduled at the instances. For example, many operating systems support scheduled batch job scheduling, e.g., using variants of the “cron” utility, which allows users to specify the times at which iterations of various tasks are to be repeated. Many users of such utilities may happen to choose iteration execution times (e.g., at midnight every night for a task that is to be done once a day) that happen to match the iteration execution times chosen for other tasks and/or by other users at other instances, even though there may be no real need for all the tasks to be executed at the same time. Although any one batch job may not necessarily consume a lot of resources, contention for shared resources may rise due to hundreds or thousands of such jobs being scheduled at about the same time, and this may have a negative impact on other applications and on the batch jobs themselves.
While embodiments are described herein by way of example for several embodiments and illustrative drawings, those skilled in the art will recognize that embodiments are not limited to the embodiments or drawings described. It should be understood, that the drawings and detailed description thereto are not intended to limit embodiments to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include,” “including,” and “includes” mean including, but not limited to.